Semiconductor light emitting devices, such as Light Emitting Diodes (LEDs) or laser diodes, are widely used for many applications. As is well known to those having skill in the art, a semiconductor light emitting device includes a semiconductor light emitting element having one or more semiconductor layers that are configured to emit coherent and/or incoherent light upon energization thereof. As is well known to those having skill in the art, a light emitting diode or laser diode, generally includes a diode region on a microelectronic substrate. The microelectronic substrate may be, for example, gallium arsenide, gallium phosphide, alloys thereof, silicon carbide and/or sapphire. Continued developments in LEDs have resulted in highly efficient and mechanically robust light sources that can cover the visible spectrum and beyond. These attributes, coupled with the potentially long service life of solid state devices, may enable a variety of new display applications, and may place LEDs in a position to compete with the well entrenched incandescent and fluorescent lamps.
Much development interest and commercial activity recently has focused on LEDs that are fabricated in or on silicon carbide, because these LEDs can emit radiation in the blue/green portions of the visible spectrum. See, for example, U.S. Pat. No. 5,416,342 to Edmond et al., entitled Blue Light-Emitting Diode With High External Quantum Efficiency, assigned to the assignee of the present application, the disclosure of which is hereby incorporated herein by reference in its entirety as if set forth fully herein. There also has been much interest in LEDs that include gallium nitride-based diode regions on silicon carbide substrates, because these devices also may emit light with high efficiency.
The efficiency of conventional LEDs may be limited by their inability to emit all of the light that is generated by their active region. When an LED is energized, light emitting from its active region (in all directions) may be prevented from exiting the LED by, for example, a non-transparent wire bond pad. Typically, in gallium nitride based LEDs, a current spreading contact layer is provided to improve the uniformity of carrier injection across the cross section of the light emitting device. Current is injected into the p-side of the LED through the bond pad and the p-type contact. Light generated in an active region of the device is proportional to the carrier injection. Thus, a substantially uniform photon emission across the active region may result from the use of a current spreading layer, such as a substantially transparent p-type contact layer. However, a wire bond pad is typically not a transparent structure and, therefore, photons emitted from the active region of the LED that are incident upon the wire bond pad may be absorbed by the wire bond pad. For example, in some instances approximately 70% of the light incident on the wire bond pad may be absorbed. Such photon absorption may reduce the amount of light that escapes from the LED and may decrease the efficiency of the LED.